Electrical resistance



June 24, 1930.

E. R. STOEKLE 1,767,715

ELECTRICAL RES ISTANCE File'd Feb. 19, 1927 .IIII""""Imlllmlll'l""""ll'F I G 5 F l 6. 6

FIG. 7. 2 5 3 INVENTOR WWW Patented June 24, 1930 UNITED s ATEs PATENTOFFICE EBWIN R. STOEKLE,- F MILWAUKEE,

WISCONSIN, ASSIGNOR TO CENTRAL RADIO ELECTRICAL RESISTANCE Applicationfiled February 19, 1927. Serial No. 169,425.

This invention relates to improvements in electrical resistances andmethods of making the same. i ity, it is particularly applicable tomaking resistances of high value, having a minimum of electricalinductance, and is therefore especially adapted for use in the radioart.

One object of the invention is to provide an improved electricalresistance in which the conducting element consists of a thin Conductingpath deposited, sprayed, or other wise applied upon an insulating core,and having in the final product a spiral or heli cal form, a reflex,that is, a sinuous or tortuous form, or such other form as may bestadapt the electrical resistance to the particu- 1211' use to which it isto be put.

Another object is to provide an improved and simple method ofconstructing a resistance having a high resistance compared to itsinductance.

Another object is to provide a high electrical resistance without theuse of a large number of turns of fine wire, thus simplifying theconstruction and also decreasing the amount of self induction.

Other objects and advantages reside in certain novel features of theconstruction, arrangement and combination of parts which will behereinafter more fully described and particularly pointed out in theappended claims, reference being had to the accompanying drawing forminga part of this specification, and in which;

Figure 1 is a view in elevation showing a preferred form of a resistanceunit embodying the invention.

Figure 2 is a view in end elevation over the resistance unit shown inFigure 1.

Figure 3'is an enlarged longitudinal sectional view of a portion of theresistance unit shown in Figures 1 and 2.

Figure 4 is a perspective view showing another form of the resistanceunit.

Figure-5' is a similar view of still another form of the resistanceunit.

Figure 6 is a perspective view illustrating an elemental form of theresistance unit.

Figure 7 is a. longitudinal sectional view 0 showing a variation of-aform of the re- Although having wide adaptabil-- meter of the thread iscut down.

sisgance unit illustrated in Figures 1 to 3, an

Figure 8 shows another embodiment of the invention.

Referring to Figure l, the cylindrical core 1 is made of an insulatingmaterial such as Lavite or porcelain. The surface of this core isspirally grooved or threaded, except for the ends which are left with aplain cylindrical surface. The surface of this core is coated with athin layer of conducting material in such a manner that the walls of thegroove formed by the thread, are also coated. This may be accomplishedby first coating the core with a thin layer of graphite and then e1.ctro-plating it with nickel or other suitable metal. A metallic coatingmay be applied by spra ing the surface of the core with finely divi edmolten metal, in accordance with the Schoop recess. The thickness of thecoating Wlll determine partly the resistance which it is desired toobtain. After the core is coated, it is provided with suitable terminals2 and 3, which are pressed into intimate contact with the conductingcoating or soldered thereto.

The unit is then mounted in a lathe and the surface cut down or grounddown so that the sharp outerdiameters of the threads are completelyremoved. This will leave a spiral conducting layer in the groove formedby the thread, as shown at 4 (Figure l) and will result in increasingthe resistance a great many times. The conducting coating remaininginside the groove is better shown in the Figure 3 wherein it isexaggerated and enlarged for purposes of illustration.

Referring to Figure 3, the conducting coating 4 is shown lying in theconvolutions of the groove on the insulating core. It will be observedthat the V-shaped cross section of this conducting coating will bedecreased in proportion as the outside dia- In this manner theresistance of the unit may be increased to any desired value by varyingthe amount to which the threads are cut down. A further control of theresistance may be obtained by cutting down only a portion of thethreads'and leaving the remainder of the surface in its initialcondition as indicated at S in Figure 7 so that the current on thisun-cut surface will not pass in a spiral path along the groove but willpass directly from the roove to groove over the tops of the threads. Inthis manner a threaded core, which has been coated, may be used to makea large number of desired values of resistance greater than the initialresistance of the coated core.

By giving the core a very thin coating and then cutting the threads downrather close to their root diameter, it is possible to obtain a veryhigh resistance with relatively few convolutions of the conducting pathas compared with a wire wound resistance of the same value. This resultsin a resistance having a very much smaller value of electricalinductance than a wire wound unit of the same resistance value.

In the unit shown in Figure 4 the ratio of the inductance to theresistance is further decreased by making the core 9 of a rectangulartransverse section: In this form of the device the spiral grooves 6 arepreferably moulded on the core 9. Terminal blocks 7 and 8 are inelectrical contact with the conducting surface which carries the currentto the conducting layer in the grooves. The inductanceof thisconstruction is decreased because of the fact that the ratio of thecross sectional area of the core to the length of one turn of the spiralis greatly decreased.

Figure 5 shows a flat form of the resistance in which the grooves 10 arereflexed back and forth on the surface of the insulat-- ing base 11.These grooves are preferably moulded on the base. After coating theentire surface including the surface of the grooves, the flat surface ofthe base is held against a grinding wheel. This operation removes thecoating on the ridges separating the grooves and leaves a reflexed,thatis, a tortuous or sinuous conducting coating in the grooves as shownat 10*. Ad ustment of the resistance is again made by the degree towhich the surface is ground down. Terminal blocks 12 and 13 are providedfor leading the current into the conducting surface in the grooves. Theconstruction shown in Figure 5 will give a ratio of inductance toresistance of practically zero value, which in certain radioapplications is of considerable advantage.

In Figure 6 an elemental form of the invention is shown and asillustrated comprises an insulating base 15 having longi tudinal grooves16 therein. The groove 16 may be of any suitable cross sectional shapeand in the embodiment illustrated is a V- shape in cross section. As inthe other forms of the invention a metallic coatingis applied to thewalls of the groove and to at least the portions of the upper surface ofthe base which are contiguous to the groove 16. The upper surface of thebase is then ground away to remove the portions of the metallic coatinglying on the upper surface of the base and such portions of the base-andof the conductor in the groove as may be necessary to obtain aresistance of the desirable value.

In all embodiments of the invention, after the unit has been adjusted tothe desired value of resistance, the surface may be coated with asuitable cement or with a vitreous enamel in order to protect theresistor lying in the grooves.

In Figure 8 a spirally grooved core 1 is shown as having a continuouscoating 4? thereon. By having a spirally grooved or a groovedcore with athin coating of this character thereon the effective length of thecoating and consequently the value of the resistance is markedlyincreased without having an unduly long unit.

It will be apparent to those skilled in the art, that other forms of theinsulating core may be used to meet the conditions required withoutdeparting from the scope or spirit of my invention as defined in theappended claims.

What I claim as new and desire to secure by Letters Patent is:

1 The method of making an electrical resistance which comprises coatinga spirally grooved insulating core with a thin layer of conductingmaterial and then removing said coating from the spiral ridges on saidcore to leave a helical conducting coating in said grooves and providingsuitable terminals for making electrical connections to said conductingcoating.

2. The method of making an electrical resistance which comprises coatingwith an electrically conducting layer, the entireperipheral surface ofan insulating base having communicatingadjacent grooves, removingsaid'layer from the ridges separating-said adjacent grooves, so that theconducting layer remaining in said grooves forms a tortuous path on thesurface of said base thereby forming a high resistance path forelectrical current.

3. The method of making an electrically conductinghelix which comprisescoating a helically grooved insulating core with a layer of conductingmaterial, and then removing said coating from the helical ridgesseparating said grooves.

4. The method of making and adjusting an electrical resistance whichcomprises forming adjacent communicating V-shaped grooves on the surfaceof an insulating base,

coating said surface and grooves with a layer of conducting material,and then re moving the ridges separating said adjacent grooves until theelectrical resistance of the conducting path remaining in said grooveshas the desired value.

5. A method of .making an electrical resistance which consists inapplying a coating of conducting material to an entire surface of aninsulating body having a groove which traverses and advances along thesame and then removing the portions of the coating that occurs betweenthe traversing portions of the groove.

6. The method of making and varying an electrical resistance to adesired value which consists in applying a coating of conductingmaterial to a body of insulating material having a groove therein whichwinds around and along the same and which has a sloping wall, and thenremoving portions of the coating and portions of the insulating body tolaterally separate the portions of the conducting material that occupyadjacent portions of the groove to the desired extent and to reduce thecross sectional area of the coating to the desired extent.

7. In the art of making electrical resistances having insulating bodiesprovided with grooves narrowing toward their bottom and havingconducting coatings applied to the grooves the step of varying the valueof the resistance which consists in simultaneously removing portions ofthe conducting coatings applied to the groove and portions of theinsulating body forming the walls of said grooves.

-8. A method of making an electrical resistance which consists inapplying a coating of conducting material to an entire surface of agrooved insulating body and grinding away all of the conducting materialoutside of the groove. I

9. The method of making an electrical resistance which consists incoating .an interrupted or uneven surface of an insulating body with a'thin layer of conducting ma terial and removing a continuous strip ofthe conductin material from high portions of the coated body whereby toexpose a continuous strip of said insulating body to increase the'lengthof the -conducting path of the conducting material.

10. The method of making an electrical v resistance of a definite valuewhich consists in providing an insulating body with a groove so that thebody has an interrupted surface, placing a thin layer of conductingmaterial in the groove so that only thin edges thereof pro ect from'thegroove into the interrupted surface of the insulating body and removinga portion of the conducting material along suchan edge until the desiredvalue of resistance is obtained;

11. The. method of making an electrical resistance of a definite valuewhich consists in providing an insulating vbody with a groove so thatthe body has an interrupted surface, placing conducting material in saidgroove so that the main portion thereof is beneath the interruptedsurface of the body and a thin edge thereof is arranged in line withsaid interrupted surface and removing a portion of the conductingmaterial along said thin edge.

12. The method of making an electrical resistance which comprisesapplying a coating of conducting material to an insulating body ofirregular shape so that a thin portion of the conducting materialrojects outwardly from the insulating b0 y and from the main portion ofthe conducting material,

and removing some of the conducting material along said thin outwardlyprojecting portion.

13. An electrical resistance unit including an insulating supportingmember having a groove therein and a thin layer of comminuted conductingmaterial mounted in the groove and having an interrupted edge in linewith the interrupted surface of said supporting member.

14:. Arm electrical resistance unit including an insulating supportingmember having a groove therein so as to provide an interrupted surfaceand a thin layer of conducting material having'a graphite base mountedin the groove and having an interrupted edge in line with theinterrupted surface of said supporting member.

:Inwitness whereof, I hereto affix my signature.

ERWIN R. STOEKLE

